The invention relates to a method for determining an operating range of an ultrasonic vibration device, which ultrasonic vibration device is supplied with electrical energy by a generator via an output and is induced to vibrate ultrasonically, wherein at least components of the ultrasonic vibration device, preferably an ultrasonic transducer contained in said ultrasonic vibration device, and components of the generator, preferably an output-side matching network, form a tuned circuit.
Furthermore, the invention relates to a circuit arrangement for performing a method according to the invention, having an ultrasonic vibration device, which ultrasonic vibration device is connected to a generator and can be supplied with electrical energy by the generator via an output and can be induced to vibrate ultrasonically, wherein at least components of the ultrasonic vibration device, preferably an ultrasonic transducer contained in said ultrasonic vibration device, and components of the generator, preferably an output-side matching network, form a tuned circuit.
Ultrasonic vibration devices (also referred to as ultrasonic vibration systems) are used not only in the field of ultrasonic cleaning but also in other fields of technology, such as ultrasonic welding or cutting, for example. In addition to an ultrasonic generator, which induces the vibrations by excitation using a high-frequency electrical signal, a vibration device is necessary, which vibration device comprises an ultrasonic transducer (for example a piezo transducer) or interacts with same, which ultrasonic transducer converts electrical oscillations into mechanical vibrations. Furthermore, the vibration device additionally comprises the actual ultrasonic vibrator or emitter, or a sonotrode, which outputs the actual ultrasonic vibrations to a medium or a tool.
Vibration devices or ultrasonic transducers and the ultrasonic generator with its electrical matching network together form an electromagnetic tuned circuit. Depending on the area of application, the vibration devices can be configured in various geometric shapes and sizes and in various materials, wherein they have different operating ranges due to their shape and composition and the modified properties of said tuned circuit concomitant with said shape and composition, to which the required optimum operating frequency relates. These operating ranges can be defined or limited in the frequency domain by resonant points (resonant frequencies) in the vibration behavior, so-called parallel and series resonance. When the resonant points are known, along with the generator and vibration device, the optimum operating range of an ultrasonic device equipped therewith can be determined.
If it is necessary to exchange the vibration device, a new vibration device or the corresponding tuned circuit generally does not have the same starting frequency or the same operating range as the vibration device used previously. “Starting frequency” is to be understood as that excitation frequency of the generator at which the vibration device is initially excited during start-up of a corresponding ultrasonic device. The starting frequency should in particular be chosen such that the device or the vibration device is not damaged. In addition, changes to external parameters, for example large temperature fluctuations, result in a shift of resonant points of the vibration device or of the entire tuned circuit. Without knowledge of the resonant points, the operating range of the entire apparatus is not known.
Accordingly, in the event of an exchange or said changes, the starting frequency must often be recalculated and the operating range correspondingly reset. For this purpose, appropriate measuring tools, such as impedance analyzers, are necessary; however, they are expensive and complex to operate. The ultrasonic vibration device cannot be properly used without appropriate adjustment, however.
One possibility known from the prior art for determining the resonant points on-site and, furthermore, for ensuring correct operation of the vibration device consists in calculating the resonant points using a frequency scan of a frequency range with noise emission in the idling state, that is to say with freely vibrating vibration device without medium or pressure and correspondingly without damping. For this purpose, the vibration device has a pulse-width-modulated signal applied thereto at low generator output, wherein a particular frequency range is scanned in the idling state. By analyzing the power, the phase and the current passage, the resonant points are calculated in order to determine the operating range. However, the noise emission in the idling state firstly requires a very high volume and, secondly, the vibration device can be damaged by excitation at too high a power and, as a result, become inoperative. Risk to the operating personnel is not ruled out, either.